Even as ghosts, they were once part of the real world. A century ago, the Homeloss fell into the Subspace, and however terrifying it is today, it was built by the craftsmen of the real world, just like Captain Duncan, who was once human before turning into a shadow of the Subspace.
To ordinary sailors, everything related to the Homeloss invariably had to be cloaked in veils of "curse" and "strangeness," as if that horrifying ghost captain was directly spawned from the Subspace, an entity without human emotions or relationships—a natural disaster roaming over the Endless Sea. In many people's minds, "Captain Duncan" was like a natural phenomenon symbolized by his mere existence, with no need to trace its origins.
Fear built high walls in the minds of mortals, preventing them from thinking about what details might lie beyond those walls.